Semiconductor device having PDA function

ABSTRACT

Disclosed herein is a semiconductor device that includes a command decoder activating a first mode register setting signal in response to a mode register setting command supplied from outside, a first latency shifter activating a second mode register setting signal after elapse of predetermined cycles of a clock signal since the first mode register setting signal is activated, and a mode register storing a mode signal supplied from outside in response to the second mode register setting signal.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device and aninformation processing system including the same, and more particularlyto a semiconductor device including a mode register for setting anoperation mode and the like and an information processing systemincluding the same.

2. Description of Related Art

Some semiconductor memory devices, typified by a DRAM (Dynamic RandomAccess Memory), include a mode register for setting their operation mode(see Japanese Patent Application Laid-Open No. 2002-133866). Operationmodes to be set in the mode register may include the values of anadditive latency (AL), a CAS latency (CL), and a CAS write latency(CWL), and the impedances of output buffers (see Japanese PatentApplication Laid-Open Nos. 2008-60641 and 2009-217926).

DDR4 (Double Data Rate 4) DRAMs have recently been proposed as DRAMseven faster than DDR3 (Double Data Rate 3) DRAMs. DDR4 DRAMs support anew function called “PDA”. The PDA function provides a latency for therewriting of the mode register and makes it possible to set the moderegisters of DRAM chips to respective different values.

A circuit for implementing the PDA function and a method for controllingthe same need to have a simple circuit configuration and be a simplecontrol method without increasing the circuit area of the semiconductordevice.

SUMMARY

In one embodiment, there is provided a semiconductor device thatincludes: a command decoder activating a first mode register settingsignal in response to a mode register setting command issued fromoutside; a first latency shifter activating a second mode registersetting signal after elapse of predetermined cycles of a clock signalsince the first mode register setting signal is activated; and a moderegister storing a mode signal supplied from outside in response to thesecond mode register setting signal.

In another embodiment, there is provided a semiconductor device thatincludes: a command decoder activating a first mode register settingsignal in response to a mode register setting command issued fromoutside; a latency shifter delaying the first mode register settingsignal to generate a second mode register setting signal; a logic gatecircuit that activates a third mode register setting signal in responseto the second mode register setting signal when a data signal suppliedfrom outside is in a first logic level, and inactivates the third moderegister setting signal regardless of the second mode register settingsignal when the data signal is in a second logic level; and a moderegister storing a mode signal in response to the third mode registersetting signal.

In still another embodiment, there is provided a semiconductor devicecomprising: a first external terminal receiving a command signal; asecond external terminal receiving a data signal; a third externalterminal receiving an address signal; a command decoder configured tooutput a mode register setting signal based on the command signal; alatency shifter configured to receive the mode register setting signaland output a shifted mode register setting signal; a logic gateconfigured to receive the shifted mode register setting signal and aportion of the data signal and output a second mode register settingsignal; and a mode register configured to receive the second moderegister setting signal and a portion of the address signal.

In still another embodiment, there is provided an information processingsystem that includes: a plurality of semiconductor devices; and acontroller that supplies a mode register setting command and a modesignal to the plurality of semiconductor devices in common, and suppliesdifferent data signals to each of the semiconductor devices. Each of thesemiconductor devices includes: a command decoder activating a firstmode register setting signal in response to the mode register settingcommand supplied from the controller; a latency shifter delaying thefirst mode register setting signal to generate a second mode registersetting signal; a logic gate circuit that activates a third moderegister setting signal in response to the second mode register settingsignal when an associated one of the data signals supplied from thecontroller is in a first logic level, and inactivates the third moderegister setting signal regardless of the second mode register settingsignal when the associated one of the data signal is in a second logiclevel; and a mode register storing the mode signal supplied from thecontroller in response to the third mode register setting signal.

According to the present invention, the PDA function can be implementedby a simple circuit configuration.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram for explaining the principle of an embodiment;

FIG. 2 is an example of a truth table for explaining an operation of acommand decoder shown in FIG. 1;

FIG. 3 is a schematic diagram for explaining the connection between aplurality of semiconductor devices 10 and a controller 50;

FIG. 4 is a block diagram indicative of an embodiment of a semiconductordevice 10 a according to a first preferred embodiment of the presentinvention and mainly shows details of circuit blocks that belong to aaccess control circuit 20 shown in FIG. 1;

FIG. 5 is a circuit diagram indicative of an embodiment of a moderegister shown in FIG. 1;

FIG. 6 is a circuit diagram indicative of an embodiment of a registerset shown in FIG. 5;

FIG. 7 is a timing chart for explaining the operation of thesemiconductor device 10 a according to the present embodiment;

FIG. 8 is a block diagram indicative of an embodiment of a semiconductordevice 10 b according to a second preferred embodiment of the presentinvention and mainly shows details of circuit blocks belonging to theaccess control circuit 20 shown in FIG. 1;

FIG. 9 is a block diagram indicative of an embodiment of a semiconductordevice 10 c according to a third preferred embodiment of the presentinvention and mainly shows details of circuit blocks belonging to theaccess control circuit 20 shown in FIG. 1;

FIG. 10 is a circuit diagram indicative of an embodiment of an FIFOcircuit 200; and

FIG. 11 is a timing chart for explaining the operation of thesemiconductor device 10 c according to the third embodiment.

DETAILED DESCRIPTION OF THE EMBODIMENTS

A representative example of the technical concept of an embodiment ofthe present invention for solving the problem will be described below.It will be understood that what the present invention claims are notlimited to such a technical concept but set forth in the claims of thepresent invention. The technical concept of the present embodimentincludes: activating a mode register setting signal based on a moderegister setting command issued from a controller; delaying the moderegister setting signal as much as a predetermined latency by using alatency shifter; and then rewriting a mode register based on the delayedmode register setting signal. This can provide a latency for therewriting of the mode register. Whether to enable or disable the moderegister setting signal may be specified by supplying a data signal ofhigh level or low level to the semiconductor device in synchronizationwith a lapse of the latency. Consequently, even if a plurality ofsemiconductor devices are connected to a single controller in common,set values can be written into the mode registers of the respectivesemiconductor devices.

Referring now to FIG. 1, an information processing system including acontroller 50 and a semiconductor device 10 is shown. The semiconductordevice 10 shown in FIG. 1 is a semiconductor memory device such as aDRAM. The semiconductor device 10 includes a memory cell array 11. Thememory cell array 11 is divided, though not limited to, into a pluralityof bank groups. Each bank group is divided into a plurality of banks.The memory cell array 11 includes a plurality of word lines WL and aplurality of bit lines BL which intersect each other. Memory cells MCare arranged at the intersections. The word lines WL are selected by arow decoder 12. The bit lines BL are selected by a column decoder 13.The bit lines BL are connected to respective corresponding senseamplifiers SA in a sense circuit 14. Bit lines BL selected by the columndecoder 13 are connected to an amplifier circuit 15 through senseamplifiers SA.

The operation of the row decoder 12, the column decoder 13, the sensecircuit 14, and the amplifier circuit 15 is controlled by an accesscontrol circuit 20. An address signal ADD, a command signal CMD, a chipselect signal CS, and a clock signal CK are supplied to the accesscontrol circuit 20 through terminals 21 to 24. Based on such signals,the access control circuit 20 controls the row decoder 12, the columndecoder 13, the sense circuit 14, the amplifier circuit 15, and a datainput/output circuit 30.

Specifically, if the command signal CMD is an active command, theaddress signal ADD is supplied to the row decoder 12. In response tothis, the row decoder 12 selects a word line WL that is designated bythe address signal ADD, whereby corresponding memory cells MC areconnected to respective bit lines BL. The access control circuit 20 thenactivates the sense circuit 14 at predetermined timing.

On the other hand, if the command signal CMD is a read command or awrite command, the address signal ADD is supplied to the column decoder13. In response to this, the column decoder 13 connects bit lines BLdesignated by the address signal ADD to the amplifier circuit 15.Consequently, in a read operation, read data DQ read from the memorycell array 11 through sense amplifiers SA is output from a data terminal31 to outside through the amplifier circuit 15 and the data input/outputcircuit 30. In a write operation, write data DQ supplied from outsidethrough the data terminal 31 and the data input/output circuit 30 iswritten to memory cells MC through the amplifier circuit 15 and senseamplifiers SA.

As shown in FIG. 1, the access control circuit 20 includes an addresslatch circuit 81, a command decoder 82, a latency shifter 83, and a moderegister 84.

The address latch circuit 81 is a circuit that latches the addresssignal ADD supplied through the address terminal 21. As described above,the address signal ADD latched in the address latch circuit 81 issupplied to the row decoder 21 or the column decoder 13 depending on thecontent of the command signal CMD.

The command decoder 82 is a circuit that decodes the command signal CMDand the chip select signal CS supplied through the command terminal 22and the chip select terminal 23. The command signal CMD includes, thoughnot limited to, a plurality of bits of control signals including anactive signal ACT, a row address strobe signal RAS, a column addressstrobe signal CAS, and a write enable signal WE. Access types aredefined by the combinations of the logic levels of such signals.Examples of the access types include a row access based on an activecommand, a read access based on a read command, a write access based ona write command, a rewrite operation on a mode register based on a moderegister setting command, and a status quo operation based on a NOPcommand.

Turning to FIG. 2, in this example, combinations of the chip selectsignal CS and the command signal CMD produce internal commands includinga DESEL command, the NOP command, an active command IACT, a prechargecommand IPRE, a first write command IWR1, a read command IRD1, and afirst mode register setting command MRS1. As employed herein, an activesignal IACT is a signal that indicates the active command IACT. A firstwrite signal IWR1 is a signal that indicates the first write commandIWR1. A read signal IRD1 is a signal that indicates the read commandIRD1. A first mode register setting signal MRS1 is a signal thatindicates the first mode register setting command MRS1.

The DESEL command is a command that is generated when the chip selectsignal CS is in an inactive state. When the DESEL command is issued, theaccess control circuit 20 performs no access operation. The NOP commandis a command that is generated when the chip select signal CS is in anactive state and all the bits of the command signal CMD are at a lowlevel. Again, when the NOP command is issued, the access control circuit20 performs no access operation.

When the active command IACT, the first write command IWR1, and the readcommand IRD1 are issued, the access control circuit 20 performs theforegoing operations to make a row access, a write access, and a readaccess, respectively. The precharge command IPRE is a command fordeactivating the memory cell array 11 which has been activated by theactive command IACT. The first mode register setting signal MRS1 is aninternal command for rewriting a set value of the mode register 84.

The first mode register setting command MRS1 is supplied to the latencyshifter 83. The latency shifter 83 is a circuit that delays the firstmode register setting signal MRS1 by a predetermined latency insynchronization with the clock signal CK supplied through the clockterminal 24. The first mode register setting signal MRS1 delayed by thelatency shifter 83 is supplied to the mode register 84 as a second moderegister setting signal MRS2. In the present embodiment, the latencyshifter 83 maybe referred to as a “first latency shifter”.

The mode register 84 is rewritten with a mode signal supplied from theaddress terminal 21 at the activation timing of the second mode registersetting signal MRS2. Note that the overwrite operation on the moderegister 84 is enabled or disabled depending on the logic level of adata signal D0. Specifically, if the data signal D0 is at a low level,the overwrite operation on the mode register 84 is enabled. If the datasignal D0 is at a high level, the overwrite operation on the moderegister 84 is disabled. As described above, the second mode registersetting signal MRS2 is activated after a lapse of a predeterminedlatency since the activation of the first mode register setting signalMRS1. The data signal D0 is therefore also input after a lapse of apredetermined latency since the issuance of the mode register settingcommand. The data signal D0 refers to a signal that is input from one ofdata terminals 31 if there are a plurality of data terminals 31.

The foregoing circuit blocks operate with respective predeterminedinternal voltages as their power supply. The internal power supplies aregenerated by a power supply circuit 40 shown in FIG. 1. The power supplycircuit 40 receives an external potential VDD and a ground potential VSSsupplied through power supply terminals 41 and 42, respectively. Basedon the potentials, the power supply circuit 40 generates internalvoltages VPP, VPERI, VARY, etc. The internal potential VPP is generatedby boosting the external potential VDD. The internal potentials VPERIand VARY are generated by stepping down the external potential VDD.

The internal voltage VPP is a voltage that is mainly used in the rowdecoder 12. The row decoder 12 drives a word line WL that is selectedbased on the address signal ADD to the VPP level, thereby making thecell transistors included in memory cells MC conducting. The internalvoltage VARY is a voltage that is mainly used in the sense circuit 14.The sense circuit 14, when activated, drives either one of each pair ofbit lines to the VARY level and the other to the VSS level, therebyamplifying read data that is read out. The internal voltage VPERI isused as the operating voltage of most of the peripheral circuits such asthe access control circuit 20. The use of the internal voltage VPERIlower than the external voltage VDD as the operating voltage of theperipheral circuits reduces the power consumption of the semiconductordevice 10.

Now, the controller 50 includes an output circuit 60 and a dataprocessing circuit 70. The output circuit 60 is a circuit for supplyingthe address signal ADD, the command signal CMD, the chip select signalCS, and the clock signal CK to the semiconductor device 10 throughterminals 61 to 64. The data processing circuit 70 is a circuit thatprocesses read data DQ and write data DQ input/output through a dataterminal 71. The controller 50 issues a mode register setting command tothe semiconductor device 10, and after a lapse of a predeterminedlatency, sets the data signal D0 to a high level or low level. The datasignal D0 is a part of the write data DQ. This can specify whether toenable or disable a mode signal that is supplied along with the moderegister setting command.

Turning to the example shown in FIG. 3, the plurality of semiconductordevices 10 are divided into two ranks (RANK0 and RANK1). A chip selectsignal CS0 is supplied to a plurality of semiconductor devices 10belonging to RANK0. A chip select signal CS1 is supplied to a pluralityof semiconductor devices 10 belonging to RANK1. Either one of the chipselect signals CS0 and CS1 can be activated to select one of the ranks.As shown in FIG. 3, the data terminals 31 of the plurality ofsemiconductor device 10 belonging to the same rank are individuallyconnected to the controller 50. Consequently, read data DQ and writedata DQ are transmitted and received between the controller 50 and theplurality of semiconductor devices 10 in parallel. The data terminals 31of different ranks are connected in common, whereas the transmission andreception of read data DQ or write data DQ will not be simultaneouslyperformed on different ranks.

In the meantime, command and address system signals CA output from thecontroller 50 are supplied to all the semiconductor devices 10 incommon. The command and address system signals CA refer to a group ofsignals including the address signal ADD, the command signal CMD, andthe clock signal CK.

With such a configuration, for example, when the controller 50 issues amode register setting command, the command becomes valid to allsemiconductor devices 10 that belong to a rank selected by the chipselect signal CS0 or CS1. In other words, it is not possible toindividually issue a mode register setting command to each of aplurality of semiconductor devices 10 belonging to the same rank.

According to the present embodiment, the data signal DO can be used toindividually enable a mode register setting operation on each of aplurality of semiconductor devices 10 belonging to the same rank. As aresult, the mode registers 84 in the plurality of semiconductor devices10 belonging to the same rank can be set to respective different values.

Preferred embodiments of the present invention will be explained belowin detail with reference to the accompanying drawings.

Turning to FIG. 4, in the first preferred embodiment, the address signalADD includes bank group signals BG0 and BG1, bank address signals BA0and BA1, and address signals A0 to A16. The bank group signals BG0 andBG1 are signals for selecting any one of four bank groups included inthe memory cell array 11. The bank address signals BA0 and BA1 aresignals for selecting any one of four banks included in the selectedbank group. The address signal A0 to A16 are used as a row addressduring a row access, and as a column address during a column access.During mode register setting, the address signals A0 to A16 are used asa mode signal.

The command decoder 82 outputs the first write signal IWR1 and the firstmode register setting signal MRS1. A latency shifter 85 gives the firstwrite signal IWR1 a predetermined latency before outputting the firstwrite signal IWR1 as a second write signal IWR2. When the second writesignal IWR2 is activated, write data DQ is supplied from the controller50 and the data input/output circuit 30 shown in FIG. 1 takes in thewrite data DQ.

The latency shifter 85 is a circuit that gives a write latency WL to thefirst write signal IWR1 in synchronization with an internal clock signalICLK. The internal clock signal ICLK is a synchronization signalsynchronous with the clock signal CK supplied from the controller 50. Inthe present embodiment, the latency shifter 85 may be referred to as a“second latency shifter.”

The value of the write latency WL is set to the sum of an additivelatency signal AL and a CAS write latency signal CWL which are suppliedfrom the mode register 84. The write latency WL refers to the latencyfrom the issuance of a write command from the controller 50 to the inputof the first piece of write data DQ. Issuance timing of a write commandmay precede its original issuance timing by an additive latency (AL).The write latency WL is thus defined by WL=AL+CWL, where latency fromthe original issuance timing of the write command to the input of thefirst piece of write data DQ is the CAS write latency (CWL).

The first mode register setting signal MRS1 is supplied to AND gatecircuits G0 and G1 in common. The AND gate circuit G0 is a gate circuitthat passes the first mode register setting signal MRS1 if an enablesignal PDAen is activated to a high level. The AND gate circuit G1 is agate circuit that passes the first mode register setting signal MRS1 ifthe enable signal PDAen is deactivated to a low level. In the presentembodiment, the AND gate circuits G0 and G1 may be referred to as a“first circuit.”

The enable signal PDAen is a signal output from the mode register 84.The enable signal PDAen is activated to a high level when thesemiconductor device 10 is set to a PDA mode. The enable signal PDAen isotherwise deactivated to a low level. In the present embodiment, the PDAmode may be referred to as a “first operation mode”, and the other casesas a “second operation mode”.

A first mode register setting signal MRS1 a passed through the AND gatecircuit G0 is supplied to the latency shifter 83. The latency shifter 83is a circuit having the same function as that of the foregoing latencyshifter 85. The latency shifter 83 gives a write latency WL to the firstmode register setting signal MRS1 a in synchronization with the internalclock signal ICLK, and outputs the resultant as a second mode registersetting signal MRS2. The value of the write latency WL is set to the sumof the additive latency signal AL and the CAS write latency signal CWLwhich are supplied from the mode register 84.

The second mode register setting signal MRS2 is supplied to asynchronized delay circuit 86, which provides one clock cycle of delayin synchronization with the internal clock signal ICLK. A second moderegister setting signal MRS2 a output from the synchronized delaycircuit 86 is supplied to one of the input nodes of an AND gate circuitG3. An inverted signal of the data signal D0 is supplied to the otherinput node of the AND gate circuit G3. The output of the AND gatecircuit G3 is supplied to one of the input nodes of the OR gate circuitG2. In the present embodiment, the AND gate circuit G3 may be referredto as a “third circuit”.

A first mode register setting signal MRS1 b output from the AND gatecircuit G1 is supplied to the other input node of the OR gate circuitG2. A third mode register setting signal MRS3 output from the OR gatecircuit G2 is supplied to the mode register 84. When the third moderegister setting signal MRS3 is activated to a high level, a set valueof the mode register 84 is rewritten based on the address signal ADD. Inthe present embodiment, the OR gate circuit G2 may be referred to as a“second circuit”.

Turning to FIG. 5, the mode register 84 includes eight register sets84-0 to 84-7 and a decoder DEC which selects any one of the registersets 84-0 to 84-7. The decoder DEC is a circuit that receives a bankgroup signal XAbg0 and bank address signals XAba0 and XAba1 which arelatched in the address latch circuit 81. Based on the three selectionbits, the decoder DEC activates any one of eight bits of select signalsMR0 en to MR7 en. The select signals MR0 en to MR7 en are supplied toone of the input nodes of respective corresponding AND gate circuits G10to G17, respectively. The third mode register setting signal MRS3 issupplied to the other input nodes of the AND gate circuits G10 to G17 incommon.

The AND gate circuits G10 to G17 output select signals MR0 clk to MR7clk, which are supplied to the respective corresponding register sets84-0 to 84-7. The register sets 84-0 to 84-7 are overwritten with a modesignal using a row address XA0 to XA12 if the respective correspondingselect signals MR0 clk to MR7 clk are activated. Set values MR0 to MR7set in the register sets 84-0 to 84-7 are supplied to respectivepredetermined circuit blocks, whereby the operation mode of thesemiconductor device 10 is specified.

Turning to FIG. 6, the register set 84-0 includes 13 registers 100 to112. The input nodes D of the registers 100 to 112 are supplied with therespective corresponding bits of the mode signals XA0 to XA12. Theselect signal MR0 clk is supplied to the clock nodes of the registers100 to 112 in common. With such a configuration, when the select signalMR0 clk is activated to a high level, the mode signals XA0 to XA12 areset into the registers 100 to 112. The set values of the registers 100to 112, or bits MR0_0 to MR0_12, are output as a 13-bit signal thatconstitutes a set value MR0. The other register sets 84-1 to 84-7 havethe same circuit configuration as that of the register set 84-0 shown inFIG. 6 except in that the select signals MR1 clk to MR7 clk are suppliedinstead of the select signal MR0 clk.

The circuit configuration of the semiconductor device 10 a according tothe present embodiment has been described so far. Next, the operation ofthe semiconductor device 10 a according to the present embodiment willbe described.

Turning to FIG. 7, in this example, mode register setting commands areissued at times t11, t12, and t14. When a mode register setting commandis issued at time t11, the bank group signal BG0 and the bank addresssignals BA0 and BA1 have a value of 0 (in decimal notation). The addresssignals A0 to A12 have a value A. When a mode register setting commandis issued at time t12, the bank group signal BG0 and the bank addresssignals BA0 and BA1 have a value of 1 (in decimal notation). The addresssignals A0 to A12 have a value B. When a mode register setting commandis issued at time t14, the bank group signal BG0 and the bank addresssignals BA0 and BA1 have a value of 2 (in decimal notation). The addresssignals A0 to A12 have a value C.

When a mode register setting command is issued, the command decoder 82activates the first mode register setting signal MRS1. At time t11, theenable signal PDAen is at a low level. The first mode register settingsignal MRS1 a is therefore not activated, and the first mode registersetting signal MRS1 b is activated. The activation of the first moderegister setting signal MRS1 b immediately activates the third moderegister setting signal MRS3, whereby the designated register set 84-0is overwritten with the mode signal A.

At time t12, the enable signal PDAen is at a high level, and the firstmode register setting signal MRS1 a is thus activated. The first moderegister setting signal MRS1 a is input to the latency shifter 83, andafter a lapse of the write latency WL, output as the second moderegister setting signal MRS2 (time t13). In the present example, thedata signal D0 is set to a low level at timing one clock cycle aftertime t13. As a result, the third mode register setting signal MRS3 isactivated, and the designated register set 84-1 is overwritten with themode signal B.

At time t14, the enable signal PDAen is again at a high level, whichactivates the first mode register setting signal MRS1 a. The first moderegister setting signal MRS1 a is input to the latency shifter 83, andafter a lapse of the write latency WL, output as the second moderegister setting signal MRS2 (time t15). In the present example, thedata signal D0 is at a high level at timing one clock cycle after timet15. Since the third mode register setting signal MRS3 is maintained inan inactive state, the designated register set 84-2 is not overwrittenwith the mode signal C.

As described above, according to the present embodiment, the PDAfunction for DDR4 DRAMs to support can be implemented by a simplecircuit configuration.

Next, the second preferred embodiment of the present invention will bedescribed.

Turning to FIG. 8, components similar to those of FIG. 4 are designatedby the same reference numbers. Redundant description thereof will beomitted.

As shown in FIG. 8, in the present embodiment, the latency shifter 83 iseliminated and its function is implemented by the latency shifter 85which is for use in a write operation. For that purpose, the first moderegister setting signal MRS1 a output from the AND gate circuit G0 andthe first write signal IWR1 are supplied to an OR gate circuit G4. Theoutput of the OR gate circuit G4 is input to the latency shifter 85. Thesecond mode register setting signal MRS2 and the second write signalIWR2 output from the latency shifter 85 are an identical signal. Thefirst write signal IWR1 is output as the second write signal IWR2through the latency shifter 85. The first mode register setting signalMRS1 a is output as the second mode register setting signal MRS2 throughthe latency shifter 85. As shown in FIG. 2, the first write command IWR1and the first mode register setting command MRS1 do not occur at thesame time. The latency shifter 85 can thus be shared by the first writecommand IWR1 and the first mode register setting command MRS1. In thepresent embodiment, the OR gate circuit G4 may be referred to as a“fourth circuit”. The second mode register setting signal MRS2 outputfrom the latency shifter 85 is supplied to one of the input nodes of anAND gate circuit G5. The enable signal PDAen is supplied to the otherinput node of the AND gate circuit G5. The output of the AND gatecircuit G5 is supplied to the synchronized delay circuit 86. In thepresent embodiment, the AND gate circuit G5 may be referred to as a“fifth circuit”. In other respects, the circuit configuration is thesame as that of the semiconductor device 10 a according to the firstembodiment shown in FIG. 4.

According to the present embodiment, the latency shifter 85 for use in awrite operation is utilized to delay the first mode register settingsignal MR51 a. A dedicated latency shifter therefore need not be added.This provides the effect of a reduction in chip area in addition to theeffects of the first embodiment.

Next, the third preferred embodiment of the present invention will bedescribed.

Turning to FIG. 9, components similar to those of FIG. 8 are designatedby the same reference numbers. Redundant description thereof will beomitted.

As shown in FIG. 9, an FIFO circuit 200 for delaying an address signalis added in the present embodiment. The FIFO circuit 200 is apoint-shift FIFO circuit using an in-pointer 220 and an out-pointer 230.A selector 240 selects an address signal Ain to be input to the FIFOcircuit 200. A column address signal YA, the bank group signal XAbg0 andbank address signals XAba0 and XAba1 (selection bits), and the rowaddress XA0 to XA12 (mode signal) are supplied to the selector 240. Theselector 240 selects either the column address signal YA or the othersbased on the enable signal PDAen. Specifically, if the enable signalPDAen is activated to a high level, the selector 240 selects theselection bits and the mode signal. If the enable signal PDAen isdeactivated to a low level, the selector 240 selects the column addresssignal YA. In the present embodiment, the selector 240 may be referredto as a “sixth circuit”.

An address signal Aout output from the FIFO circuit 200, the selectionbits, and the mode signal are supplied to a selector 250. If the enablesignal PDAen is activated to a high level, the selector 250 selects theaddress signal Aout. If the enable signal PDAen is deactivated to a lowlevel, the selector 250 selects the selection bits and the mode signal.In the present embodiment, the selector 250 may be referred to as a“seventh circuit”.

Consequently, in a PDA mode, the selection bits and the mode signalpassed through the FIFO circuit 200 are supplied to the mode register84. When not in the PDA mode, the selection bits and the mode signal notpassed through the FIFO circuit 200 are supplied to the mode register84. When not in the PDA mode, the FIFO circuit 200 is used to delay thecolumn address signal YA.

Turning to FIG. 10, the FIFO circuit 200 includes four latch circuits210 to 213. The address signal Ain is supplied to the input nodes D ofthe four latch circuits 210 to 213 in common. The latch circuits 210 to213 have an enable node G. The enable nodes G are supplied withrespective corresponding enable signals en_0 to en_3. The enable signalsen_0 to en_3 are signals that a decoder 201 generates by decoding apoint signal IP which is the output of the in-pointer 220. Thein-pointer 220 is a kind of counter circuit whose value is incrementedeach time the OR gate circuit G4 outputs a command.

Output signals dat_0 to dat_3 output from the output nodes Q of thelatch circuits 210 to 213 are selected by a selector 202. The selector202 makes a selection based on a point signal OP which is the output ofthe out-pointer 230. The out-pointer 230 is a kind of counter circuitwhose value is incremented each time the latency shifter 85 outputs thecommand IWR2 or MRS2. Any one of the output signals dat_0 to dat_3selected by the selector 202 is output from the FIFO circuit 200 as theaddress signal Aout.

Turning to FIG. 11, in this example, mode register setting commands areissued at times t21, t22, t23, and t24. When a mode register settingcommand is issued at time t21, the bank group signal BG0 and the bankaddress signals BA0 and BA1 have a value of 0 (in decimal notation). Theaddress signals A0 to A12 have a value A. When a mode register settingcommand is issued at time t22, the bank group signal BG0 and the bankaddress signals BA0 and BA1 have a value of 1 (in decimal notation). Theaddress signals A0 to A12 have a value B. When a mode register settingcommand is issued at time t23, the bank group signal BG0 and the bankaddress signals BA0 and BA1 have a value of 2 (in decimal notation). Theaddress signals A0 to A12 have a value C. When a mode register settingcommand is issued at time t24, the bank group signal BG0 and the bankaddress signals BA0 and BA1 have a value of 3 (in decimal notation). Theaddress signals A0 to A12 have a value D.

When a mode register setting command is issued, the command decoder 82activates the first mode register setting signal MRS1. At time t21, theenable signal PDAen is at a low level. The third mode register settingsignal MRS3 is thus immediately activated, and the designated registerset 84-0 is overwritten with the mode signal A.

On the other hand, at times t22, t23, and t24, the enable signal PDAenis at a high level, which activates the first mode register settingsignal MRS1 a. The first mode register setting signal MRS1 a is input tothe latency shifter 83, and after a lapse of the write latency WL,output as the second mode register setting signal MRS2 (times t25, t26,and t27). In the present embodiment, even when the enable signal PDAenis activated to a high level, the controller 50 need not continuesupplying the selection bits and the mode signal until the mode signalis actually written into the mode register 84. In the presentembodiment, the selection bits and the mode signal are suppliedsimultaneously with the issuance of a mode register setting command likewhen issuing a column command. Then, a next mode register settingcommand can be issued at a minimum submission interval of columncommands (tCCD). Consequently, the selection bits and the mode signalmay also be supplied at the same time with the issuance of the command.

The selection bits and the mode signal supplied in synchronization witha mode register setting command are delayed by the FIFO circuit 200 asmuch as the write latency WL. When the second mode register settingsignal MRS2 is output from the latency shifter 85, the correspondingselection bits and mode signal are output from the FIFO circuit 200 insynchronization and supplied to the mode register 84.

At timings one clock cycle after times t25 and t26, the data signal DOis set at a low level. The register set 84-1 is thus overwritten withthe mode signal B, and the register set 84-2 is overwritten with themode signal C.

On the other hand, at timing one clock cycle after time t27, the datasignal DO is set at a high level. This prevents the designated registerset 84-3 from being overwritten with the mode signal D, and the contentof the mode register 84 is maintained.

As described above, according to the present embodiment, the FIFOcircuit 200 is used to give the selection bits and the mode signal thesame delay as that of the mode register setting signal. Mode registersetting commands can thus be issued at shorter intervals. Consequently,in addition to the effects of the second embodiment, it is possible tocomplete mode setting on the plurality of register sets 84-0 to 84-7 ina shorter time. Since the FIFO circuit 200 and the controlling pointers220 and 230 are circuits for use in a write operation, the circuit scaleincreases little.

It is apparent that the present invention is not limited to the aboveembodiments, but may be modified and changed without departing from thescope and spirit of the invention.

Volatile memories, non-volatile memories, or mixtures of them can beapplied to the memory cells of the present invention.

The technical concept of the present invention is not limited to asemiconductor device including memory cells, and may be applied to asemiconductor device including a register that retains controlinformation for controlling operation conditions and the like ofcircuits included in the semiconductor device. The forms of the circuitsin the circuit blocks disclosed in the drawings and other circuits forgenerating the control signals are not limited to the circuit formsdisclosed in the embodiments.

When the transistors are field effect transistors (FETs), various FETsare applicable, including MIS (Metal Insulator Semiconductor) and TFT(Thin Film Transistor) as well as MOS (Metal Oxide Semiconductor). Thedevice may even include bipolar transistors. For example, the presentinvention can be applied to a general semiconductor device such as a CPU(Central Processing Unit), an MCU (Micro Control Unit), a DSP (DigitalSignal Processor), an ASIC (Application Specific Integrated Circuit),and an ASSP (Application Specific Standard Circuit), each of whichincludes a memory function. An SOC (System on Chip), an MCP (Multi ChipPackage), and a POP (Package on Package) and so on are pointed to asexamples of types of semiconductor device to which the present inventionis applied. The present invention can be applied to the semiconductordevice that has these arbitrary product form and package form.

When the transistors that constitute a logic gate and the like are fieldeffect transistors (FETs), various FETs are applicable, including MIS(Metal Insulator Semiconductor) and TFT (Thin Film Transistor) as wellas MOS (Metal Oxide Semiconductor). The device may even include bipolartransistors.

In addition, an NMOS transistor (N-channel MOS transistor) is arepresentative example of a first conductive transistor, and a PMOStransistor (P-channel MOS transistor) is a representative example of asecond conductive transistor.

Many combinations and selections of various constituent elementsdisclosed in this specification can be made within the scope of theappended claims of the present invention. That is, it is needles tomention that the present invention embraces the entire disclosure ofthis specification including the claims, as well as various changes andmodifications which can be made by those skilled in the art based on thetechnical concept of the invention.

In addition, while not specifically claimed in the claim section, theapplicant reserves the right to include in the claim section of theapplication at any appropriate time the following semiconductor devicesand information processing systems:

A1. A semiconductor device comprising:

a command decoder activating a first mode register setting signal inresponse to a mode register setting command issued from outside;

a latency shifter delaying the first mode register setting signal togenerate a second mode register setting signal;

a logic gate circuit that activates a third mode register setting signalin response to the second mode register setting signal when a datasignal supplied from outside is in a first logic level, and inactivatesthe third mode register setting signal regardless of the second moderegister setting signal when the data signal is in a second logic level;and

a mode register storing a mode signal in response to the third moderegister setting signal.

A2. The semiconductor device as described in A1, wherein the data signalis supplied after the mode register setting command is issued.

A3. The semiconductor device as described in A1 or A2, wherein the modesignal is supplied simultaneously with the mode register settingcommand.

A4. The semiconductor device as described in any one of A1 to A3,wherein

the command decoder activates a first write signal in response to awrite command issued from outside, and

the latency shifter delays the first write signal to generate the secondmode register setting signal.

A5. The semiconductor device as described in any one of A1 to A4,further comprising a FIFO circuit that delays the mode signal suppliedsimultaneously with the mode register setting command,

wherein the FIFO circuit supplies the delayed mode signal to the moderegister in response to the second mode register setting signal.

A6. An information processing system comprising:

a plurality of semiconductor devices; and

a controller that supplies a mode register setting command and a modesignal to the plurality of semiconductor devices in common, and suppliesdifferent data signals to each of the semiconductor devices,

wherein each of the semiconductor devices comprising:

-   -   a command decoder activating a first mode register setting        signal in response to the mode register setting command supplied        from the controller;    -   a latency shifter delaying the first mode register setting        signal to generate a second mode register setting signal;    -   a logic gate circuit that activates a third mode register        setting signal in response to the second mode register setting        signal when an associated one of the data signals supplied from        the controller is in a first logic level, and inactivates the        third mode register setting signal regardless of the second mode        register setting signal when the associated one of the data        signal is in a second logic level; and    -   a mode register storing the mode signal supplied from the        controller in response to the third mode register setting        signal.

A7. The information processing system as described in A6, wherein thecontroller issues the mode register setting command before supplying thedata signals.

A8. The information processing system as described in A6 or A7, whereinthe controller supplies the mode signals simultaneously with the moderegister setting command.

What is claimed is:
 1. A semiconductor device comprising: a commanddecoder activating a first mode register setting signal in response to amode register setting command issued from outside; a first latencyshifter activating a second mode register setting signal after elapse ofpredetermined cycles of a clock signal since the first mode registersetting signal is activated; and a mode register storing a mode signalsupplied from outside in response to the second mode register settingsignal.
 2. The semiconductor device as claimed in claim 1, furthercomprising a plurality of address terminals supplied with the modesignal.
 3. The semiconductor device as claimed in claim 1, furthercomprising a plurality of command terminals supplied with a commandsignal constituted of a plurality of bit signals, the mode registersetting command being indicated by a predetermined logical combinationof the bit signals.
 4. The semiconductor device as claimed in claim 1,further comprising a clock terminal supplied with the clock signal fromoutside.
 5. The semiconductor device as claimed in claim 1, furthercomprising a data terminal supplied with a data signal from outside,wherein the mode register stores the mode signal in response to thesecond mode register setting signal and the data signal.
 6. Thesemiconductor device as claimed in claim 1, further comprising: a firstcircuit supplying the first mode register setting signal to the firstlatency shifter in a first operation mode, and supplying the first moderegister setting signal to the mode register without supplying to thefirst latency shifter in a second operation mode; and a second circuitthat supplies the second mode register setting signal to the moderegister in the first operation mode, and supplies the first moderegister setting signal to the mode register in the second operationmode.
 7. The semiconductor device as claimed in claim 6, wherein thefirst circuit is coupled between the command decoder and the firstlatency shifter, and the second circuit is coupled between the firstlatency shifter and the mode register.
 8. The semiconductor device asclaimed in claim 6, further comprising a data terminal supplied with adata signal from outside, wherein the mode register stores the modesignal in response to the second mode register setting signal and thedata signal in the first operation mode, and stores the mode signal inresponse to the first mode register setting signal in the secondoperation mode.
 9. The semiconductor device as claimed in claim 8,further comprising a third circuit coupled between the first latencyshifter and the mode register, the third circuit controlling whether tosupply the second mode register setting signal to the mode registerbased on the data signal.
 10. The semiconductor device as claimed inclaim 1, further comprising a delay circuit delaying the second moderegister setting signal in synchronism with the clock signal.
 11. Thesemiconductor device as claimed in claim 1, wherein the command decoderfurther activates a first write signal in response to a write commandissued from outside, and the semiconductor device further comprises asecond latency shifter activating a second write signal after elapse ofthe predetermined cycles of the clock signal since the first writesignal is activated.
 12. The semiconductor device as claimed in claim11, further comprising a data input/output circuit capturing a datasignal supplied from outside in association with the second writesignal.
 13. The semiconductor device as claimed in claim 1, wherein thecommand decoder further activates a first write signal in response to awrite command supplied from outside, the semiconductor device furthercomprises a fourth circuit coupled between the command decoder and thefirst latency shifter, the fourth circuit supplying one of the firstwrite signal and the first mode register setting signal to the firstlatency shifter, and the first latency shifter activates the second moderegister setting signal after elapse of the predetermined cycles of theclock signal since the first write signal is activated.
 14. Thesemiconductor device as claimed in claim 13, further comprising a fifthcircuit coupled between the first latency shifter and the mode register,the fifth circuit controlling whether to supply the second mode registersetting signal to the mode register.
 15. The semiconductor device asclaimed in claim 13, further comprising a FIFO circuit that stores themode signal in response to the first mode register setting signal andoutputs the mode signal stored therein in response to the second moderegister setting signal.
 16. The semiconductor device as claimed inclaim 15, further comprising: a sixth circuit supplying one of anaddress signal and the mode signal to the FIFO circuit, the addresssignal being supplied from outside in association with the first writesignal; and a seventh circuit supplying one of the mode signal passedthrough the FIFO circuit and the mode signal not passed through the FIFOcircuit to the mode register.
 17. The semiconductor device as claimed inclaim 16, wherein the sixth circuit supplies the mode signal to the FIFOcircuit in a first operation mode, and supplies the address signal tothe FIFO circuit in a second operation mode, and the seventh circuitsupplies the mode signal passed through the FIFO circuit to the moderegister in the first operation mode, and supplies the mode signal notpassed through the FIFO circuit to the mode register in the secondoperation mode.
 18. The semiconductor device according to claim 16,further comprising: a plurality of address terminals supplied with themode signal and the address signal from outside; and an address latchcircuit that latches the mode signal and the address signal suppliedthrough the address terminals, wherein the sixth circuit is coupledbetween the address latch circuit and the FIFO circuit, and the seventhcircuit is coupled between the FIFO circuit and the mode register. 19.The semiconductor device as claimed in claim 1, wherein thepredetermined cycle coincides with a write latency that indicates aperiod between when a write command is issued to the semiconductordevice and when a data signal is supplied to a data terminal fromoutside.
 20. A semiconductor device comprising: a first externalterminal receiving a command signal; a second external terminalreceiving a data signal; a third external terminal receiving an addresssignal; a command decoder configured to output a mode register settingsignal based on the command signal; a latency shifter configured toreceive the mode register setting signal and output a shifted moderegister setting signal; a logic gate configured to receive the shiftedmode register setting signal and a portion of the data signal and outputa second mode register setting signal; and a mode register configured toreceive the second mode register setting signal and a portion of theaddress signal.